The present invention relates to a recording sheet comprising a support and microcapsules containing a color former and a solvent therefor, and more particularly, to a recording sheet having a chlorinated alpha-olefin as the solvent for the color former.
Much time has been devoted to the development of recording systems wherein particular electron donating organic compounds possessing the capability of forming a color (hereinafter color former) on reaction with an acidic electron accepting compound (hereinafter color developer) are employed. These recording systems include pressure sensitive recording systems, heat sensitive recording systems, etc. For examples of these recording systems, see U.S. Pat. Nos. 2,712,507; 2,730,456; 2,730,457; 3,418,250 and 3,432,327. These systems involve a combination of a so called CB (coated back) sheet prepared by coating on a support a layer of microcapsules produced by microencapsulating oil droplets of a color former and a so-called CF (coated front) sheet prepared by coating a color developer on another sheet. In a pressure sensitive transfer recording system, the CB and CF sheets are superposed so that the microcapsule layer and the color developer layer are in contact with each other. Upon the application of pressure, the microcapsules are ruptured which releases the color former. The color former then reacts with the color developer to produce a coloration in the areas to which the pressure has been applied. In a self-contained system, a single sheet is prepared by coating one side of a support with a layer of the above-described microcapsules and a color developer.
Suitable solvents for effective use in recording systems must readily and easily dissolve the color former to be used, contribute effectively to formation of a high density coloration, exhibit low toxicity, have no unpleasant smell, have a high boiling point so as not to vaporize in a heat drying process and in a place of elevated temperature, and have a low viscosity so that the effusion thereof from the microcapsules can be freely done upon microcapsule rupture. Specific examples of solvents for the color formers employed in the aforementioned record papers include alkyl naphthylenes, alkylated diphenylalkanes, alkylated triphenyldimethanes, alkylated diphenyls, kerosene, chlorinated diphenyls, chlorinated paraffins and natural oils such as cottonseed oil, soybean oil, corn oil, olive oil, castor oil, fish oil, lard oil, and linseed oil.